Electromagnetic wave lane marker, device for detecting electromagnetic wave lane marker, and traffic system

ABSTRACT

The level of the electromagnetic waves transmitted by resonance of an electric resonator is only one hundredth that of calling radio waves of the detector. Furthermore, when an IC is mounted on the electric resonator and a modulated information code is superposed, the level of the superimposed electromagnetic waves further declines. As a result, sufficient detection directivity and detection distance could not be obtained. To address these problems, the present invention stores a cyclic coil and a capacitor used to cause an electric resonance in response to the first frequency in a sealed non-magnetic container to prevent degradation.

This Application is a U.S. National Phase Application of PCTInternational Application PCT/JP00/03272.

FIELD OF THE INVENTION

The present invention relates to a vehicle positioning system in whichthe position of the vehicle on a road is determined by detectingelectromagnetic lane markers laid under the road with an electromagneticlane marker detector installed on the vehicle.

BACKGROUND OF THE INVENTION

Information about road conditions including lanes and curves has beenprovided by such lane marks as white lines and traffic signs, anddrivers check them visually.

However, when visibility is low at night or as a result of weatherconditions, it is difficult for drivers to correctly obtain informationof the road visually, thus safety on the road can be threatened. Toprevent road hazards, magnetic nails have been tried to provide roadinformation to drivers. However, when trying to enhance detectivity ofthese magnetic nails by making them ferromagnetic, they tend to attractmetallic pieces left on the road. This increases the risk of puncture, aproblem which does not coincide with increasing performance. As such,problems regarding the magnetic nail have not yet been solved.

Electrical resonators have been sometimes used as an anti-theft device.In this field, an electrical resonator is mounted on a film and attachedto a product so that a device that can detect the electrical resonator,installed at the entrance of the shop, can detect to it. The electricalresonators have also been applied to the non-contacting card systemwhere information recorded on IC mounted on an electrical resonator isread out.

However, the level of the electromagnetic waves emitted by a resonanceof the electric resonator is very weak compared with the level ofcalling electromagnetic waves transmitted by a detector; normally it isonly about one millionth of that of the calling waves. When an IC ismounted on an electric resonator, and a modulated information code issuperposed, the level of the superposed electromagnetic waves furtherdeclines. Consequently, when transmitting and receiving theelectromagnetic waves of the same frequencies, interference of thecalling waves becomes unavoidable, thereby obstructing achievement ofsufficient directivity and detection distance.

SUMMARY OF THE INVENTION

A first electromagnetic lane marker of the present invention include anelectric resonator comprising a cyclic coil and a capacitor, whichresonates with inductive electromagnetic wave of a first frequency. Theelectromagnetic lane marker further includes a frequency conversioncircuit coupled to the electromagnetic resonator, and transmitselectromagnetic waves of a second frequency which was converted from theresonated first frequency.

A second electromagnetic lane marker of the present invention include anelectronic resonator comprising a first cyclic coil and a capacitor,which resonates with inductive electromagnetic wave of a firstfrequency, a frequency conversion circuit coupled to the electronicresonator, which converts the electromagnetic wave of the firstfrequency to electromagnetic wave of a second frequency, and a secondcyclic coil which transmits the electromagnetic wave of the secondfrequency.

A third electromagnetic lane marker of the present invention include

an electronic resonator comprising a first cyclic coil and capacitorsconnected to both ends of the first cyclic coil, which resonates withinductive electromagnetic wave of a first frequency, a frequencyconversion circuit coupled to said electronic resonator, which convertsthe electromagnetic wave of the first frequency to electromagnetic waveof a second frequency, and a second cyclic coil which transmits theelectromagnetic wave of the second frequency. And, the electricresonator, the frequency conversion circuit and the second cyclic coilare stored in a sealing container made of a non-magnetic material.

In a fourth electromagnetic lane marker, the sealing container of thethird lane marker is cylindrical with a bottom base and a lid.

A fifth electromagnetic lane marker is constructed based on the secondthrough fourth lane markers, in which the first and second cyclic coilsare formed respectively with a loop antenna and a bar antenna.

A sixth electromagnetic lane marker is constructed based on the secondthrough fourth lane markers, in which the first and second cyclic coilsare formed respectively with a bar antenna and a loop antenna.

A seventh electromagnetic lane marker is constructed based on the secondlane marker, in which the first and second cyclic coils are disposed atright angles.

An eighth electromagnetic lane marker is constructed based on the firstthrough seventh lane markers, in which the frequency conversion circuitis a frequency multiplier circuit which converts the second frequency tothe frequency of multiples times of the first frequency.

A ninth electromagnetic lane marker is constructed based on the secondthrough eighth lane markers, in which an “L-tap structure” is adoptedfor the second cyclic coil.

A tenth electromagnetic lane marker is constructed based on the firstthrough eighth lane markers, in which a “C-tap structure” is adopted forthe second cyclic coil.

An eleventh electromagnetic lane marker is constructed based on thefirst through tenth lane markers, in which the frequency conversioncircuit is formed with a parallel rectifier structure.

A twelfth electromagnetic lane marker is constructed based on the firstthrough tenth lane markers, in which the frequency conversion circuit isformed with a diode bridge.

A first electromagnetic lane marker detector of the present inventionincludes a means for transmitting electromagnetic waves of a specificfrequency as the first frequency wave, and identifying and receivingelectromagnetic waves of the second frequency converted from the firstfrequency and transmitted by the frequency conversion circuit coupled tothe electrical resonator mounted on the electromagnetic lane marker.

A second electromagnetic lane marker detector of the present inventionis constructed based on the first electromagnetic lane marker detector,in which a loop antenna is used to transmit the electromagnetic waves ofthe first frequency, and a bar antenna to receive the electromagneticwaves of the second frequency.

A third electromagnetic lane marker detector of the present invention isconstructed based on the first and second electromagnetic lane markerdetectors, in which a 8-letter shaped loop antenna is used to transmitthe electromagnetic waves of the specific first frequency.

A third electromagnetic lane marker detector of the present inventionconstructed based on the first to third electromagnetic lane markerdetectors includes a plurality of receiving antennas to receiveelectromagnetic waves of the specific second frequency and a positiondetector which maps, out the relative positions of the lane marker andthe receiving antennas by comparing the intensity of the electromagneticwaves received by the antennas.

A fourth electromagnetic lane marker detector of the present inventionconstructed based on the first through fourth electromagnetic lanemarker detectors, includes a means for monitoring the amount of lateraldeviation of the vehicle from the markers and an alarm which alerts adriver when the vehicle exceeds a predetermined threshold.

A fifth electromagnetic lane marker detector of the present inventionconstructed based on the fourth electromagnetic lane marker detector,contains a means for changing the reference deviation in terms of thethreshold distance from the lane marker, which is used as a reference toalert the driver.

A sixth electromagnetic lane marker detector of the present inventionconstructed based on the fourth and fifth electromagnetic lane markerdetectors, includes an alarm comprising one of a visible alarm, anaudible alarm such as a buzzer or a voice notification, and a vibration.

A seventh electromagnetic lane marker detector of the present inventionconstructed based on the fourth and fifth electromagnetic lane markerdetectors, includes a lateral-deviation-sensitive alarm which changesthe contents of the alerting according to the amount of the lateraldeviation.

An eighth electromagnetic lane marker detector of the present inventionconstructed based on the first through seventh electromagnetic lanemarker detectors, includes a transmitting means which is capable ofdetecting a speed of the vehicle, and when the speed is below apredetermined level, it stops transmitting the electromagnetic waves ofthe first frequency, and when above, it resumes transmission.

A ninth electromagnetic lane marker detector of the present inventionconstructed based on the first through eighth electromagnetic lanemarker detectors, has a height-specific transmitting power controllingmeans which is capable of controlling the transmitting amplifiers suchthat the transmitting power changes according to a setting height of thevehicle.

A tenth electromagnetic lane marker detector of the present inventionconstructed based on the first through ninth electromagnetic lane markerdetectors, has a height-sensitive transmitting power controlling meanswhich is capable of detecting the height of the vehicle and controls thetransmitting amplifiers such that the transmitting power changesaccording to the detected height of the vehicle.

A first vehicle positioning system of the present invention comprisesthe following elements:

1) an electromagnetic lane marker comprising the following elements:

a) an electric resonator comprising a cyclic coil and a capacitor, whichresonates with induction electromagnetic waves of a first frequency;

b) a frequency conversion circuit coupled to the electric resonator,which converts the first frequency and transmits the electromagneticwaves of the second frequency

2) an identifying and receiving means for receiving the secondelectromagnetic frequency which is converted from the first frequencytransmitted as a specific electromagnetic frequency and transmitted bythe frequency conversion circuit coupled to the electrical resonatormounted in the electromagnetic lane marker.

In a second vehicle positioning system of the present invention which isbased on the first vehicle positioning system, the electromagnetic lanemarkers are laid under the road.

According to a third vehicle positioning system, based on the secondvehicle positioning system, electromagnetic lane markers laid atpredetermined intervals support automatic driving.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an electromagnetic lane markerin accordance with a preferred embodiment of the present invention.

FIG. 2 is a circuit diagram of an electromagnetic lane marker inaccordance with a preferred embodiment of the present invention.

FIG. 3 is a circuit diagram of an electromagnetic lane marker inaccordance with another preferred embodiment of the present invention.

FIG. 4 is a circuit diagram of an electromagnetic lane marker inaccordance with still another preferred embodiment of the presentinvention.

FIG. 5 is a circuit diagram of an electromagnetic lane marker inaccordance with yet another preferred embodiment of the presentinvention.

FIG. 6 is a block diagram of an electromagnetic lane marker detector inaccordance with another preferred embodiment of the present invention.

FIG. 7 is a block diagram of an electromagnetic lane marker detector inaccordance with another preferred embodiment of the present invention.

FIG. 8 is an explanatory diagram illustrating a vehicle positioningsystem based on an electromagnetic lane marker and its detector inaccordance with preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention, are described belowin order. FIG. 1 is An exploded perspective view showing the structureof an electromagnetic lane marker in accordance with a preferredembodiment of the present invention. In FIG. 1, a first cyclic coil 1comprises a bar antenna formed by winding a wire on a cylindricalferrite. The first cyclical coil 1 and a capacitor 2 compose anelectromagnetic resonator which receives and resonates withelectromagnetic waves of the first frequency, and sends signals of theresonated first frequency to a frequency conversion circuit 3. Thefrequency conversion circuit converts signals of the first frequency tosignals of the second frequency, and send them to a second cyclic coil4. The second cyclic coil 4 transmits the received signals of the secondfrequency to the vehicle.

This construction allows the lane marker to transmit electromagneticwave of the second frequency which are different from theelectromagnetic wave of the first frequency it received. Therefore, lanemarkers can be identified without suffering interference of theelectromagnetic wave of the first frequency.

The first cyclic coil comprises a bar antenna formed by winding a wireon a cylindrical ferrite core, and the second cyclic coil, a loopantenna. When the loop antenna is disposed horizontally, the height ofthe antenna as a whole becomes low. Furthermore, the antenna caneffectively receive the electromagnetic waves transmitted by the vehiclehorizontally.

In this embodiment, the first cyclic coil and second cyclic coilcomprising a bar antenna and a loop antenna respectively are disposedsuch that their magnetic fluxes intersect at right angles. Due to thisconstruction, directions of the electromagnetic waves to be received andelectromagnetic waves to be transmitted intersect at right angles aswell, so that interference between them can be avoided.

In this embodiment, the bar and loop antennas are used respectively asthe first cyclic coil and the second cyclic coil. However, the firstcyclic coil and second cyclic coil can also be made of loop and barantennas respectively. In this case as well, by disposing the loopantenna flat, the height of the antenna as a whole can be kept low. Inaddition, the electromagnetic waves transmitted downward from thevehicle can be received and transmitted back to the vehicle effectively.

FIG. 1 also shows a cylindrical non-magnetic case 5 with a base and alid 6, also made of non-magnetic materials. These members help maintainenvironmental resistance of the lane marker by tightly sealing it.

Since the non-magnetic case 5 and its lid 6 are buried underground aftersealing the lane marker, they should be made with a material resistantto paving. To be more specific, a material is needed which would notdegrade or deformed when asphalt at 230° C. is laid upon it and need tobe resistant to weight of around 1 ton. It is preferable to use resinmaterials which do not suffer corrosion when exposed to oil and acidcontained in asphalt and concrete.

In this embodiment, the lane maker is sealed with a lid, however, it canbe integrally molded and the sealing is not limited to this method.

With reference to FIGS. 2 and 3, structure of the frequency conversioncircuit is described.

FIGS. 2 and 3 are circuit diagrams of an electromagnetic lane marker inaccordance with a preferred embodiment of the present invention. In FIG.2, the frequency conversion circuit 3, which comprises diodes 7connected parallel to each other, converts the first frequency to thesecond frequency which has the multiple value of the first frequency.When a diode bridge 8 shown in FIG. 3 is used in the frequencyconversion circuit, a center tap of the first cyclic coil is notrequired since electric current refluxes via grounded contact point ofthe diode bridge. In this way, the structure of the coil can besimplified. In FIGS. 2 and 3, “C-tap structure” is adopted for thesecond cyclic coil 4, in which the voltage is divided by the capacitors.A preferred embodiment shown in FIGS. 4 and 5 adopts a “L-tapstructure”. In this L-tap structure, voltage is divided by a tap pulledout from the center of the second cyclic coil 4. In FIG. 4, L-tapstructure is combined with the frequency conversion circuit 4 wherediodes are connected parallel to each other, and in FIG. 5, the L-tapstructure is combined with the frequency conversion circuit 4 with adiode bridge. The foregoing construction allows frequency of thereceived electromagnetic waves to be multiplied by rectifying themfull-wave or double voltage. As such, the lane marker can convertfrequencies without an oscillator circuit which requires power consumingelements. Furthermore, depending on the structure of the cyclic coil,either C-tap structure or L-tap structure can be selected.

An electromagnetic lane marker detector of a preferred embodiment isdescribed below with reference to FIG. 6. FIG. 6 is a block diagramillustrating a structure of the electromagnetic lane marker of apreferred embodiment of the present invention.

FIG. 6 shows a microprocessor 12 (hereinafter, MPU) which controls thedetector. Transmitting amplifier 13 amplifies and transmits theelectromagnetic waves of the first frequency which is the resonancefrequency of the lane marker required to be detected. A transmittingantenna 14 is a cyclic or a rectangular loop antenna. Receiving antennasare used for receiving electromagnetic waves reflected by the lanemarker. The receiving antennas 15 are tuned so that they can effectivelyreceive the electromagnetic waves of the first frequency. Receivingamplifiers 16 amplify signals received by the receiving antennas.Detection circuits 17 are disposed on the left, center and right of thevehicle. Three sets of the receiving antennas, the receiving amplifiersand the detection circuits are prepared to detect the lateral positionof the vehicle with respect to the lane markers.

In the embodiment, loop and bar antennas are used as the antennatransmitting the electromagnetic waves of the first frequency and theantenna receiving the electromagnetic waves of the second frequencyrespectively. By constructing the transmitting antenna with a loopantenna, it can be disposed more flexibly. Furthermore, when an antennawith a large loop is used, electromagnetic waves can be transmitted intoa larger area. Likewise, the bar antenna used as the receiving antennacan effectively receive electromagnetic waves sent back from the lanemarker.

The following is a description of the operation of the electromagneticlane marker detector constructed as described above.

The MPU 12 contains an oscillator circuit which oscillates theelectromagnetic waves of the first frequency “f”, a resonance frequencyof the lane marker. The transmitting amplifier 13 amplifies electricpower and sends it to the transmitting antenna 14 so that theelectromagnetic waves are continuously emitted. In the meantime, the MPU12 simultaneously receives electromagnetic waves. The receiving antennas15 are disposed in the left, center and right of the vehicle, and tunedso that they can effectively receive the electromagnetic waves of thesecond frequency. When the vehicle drives near the lane marker, the lanemarker resonates with the electromagnetic waves of the first frequencyand reflects the electromagnetic waves of the second frequency. Signalsof the electromagnetic waves transmitted by the lane marker and receivedby the receiving antennas 15 are amplified by the receiving amplifiers16 and detected by the detection circuits 17, and detected data is sentto the MPU 12. The MPU 12 compares receiving signal strength in theleft, center and right systems to detect the relative positions betweenthe lane marker and the: three receiving antenna systems (1-3). Sincethe positions of the three receiving antenna systems in the vehicle arepredetermined, the relative positions of the lane marker and the vehiclecan be detected from the relative positions of the lane marker and thereceiving antennas.

In this embodiment, a 8-letter-shaped loop antenna can be used as anantenna to transmit the electromagnetic waves of the first frequency.This 8-letter-shaped loop antenna transmits electromagnetic waves in itsvicinity. Meanwhile, in a distance from the transmitting antenna, theelectromagnetic waves transmitted from each of the two loops of the8-letter-shaped antenna interfere with each other since their phases aredifferent, and as a result, the influence of the electromagnetic waveson the outside of the system is mitigated.

Another embodiment of the present invention is described below. FIG. 7is a block diagram illustrating another embodiment of the presentinvention. In the diagram, the MPU 12 includes a lateral deviationmonitor which monitors lateral deviation of the vehicle and when theposition of the vehicle with respect to the lane marker exceeds apredetermined threshold, signals are sent to an alarm 25. When receivingsignals, the alarm 25 alerts the driver that the vehicle is beginning tomove out of the lane. To alert the driver, such means as a buzzer and analarm can be used. It is also possible to alert the driver by lightingor flashing a lamp, indicating on a display of the car navigationsystem, or vibrating the driver seat. This alerting will draw thedriver's attention to the situation and adjust the driving course beforethe vehicle moves totally out of the lane.

The lateral deviation monitor of this embodiment detects the position ofthe vehicle which is beginning to deviate laterally with respect to thelane marker fixed to the predetermined position by detecting theintensity of the electromagnetic waves transmitted from the lane marker.In FIG. 7, the three receiving antennas 15 (1, 2, and 3) arerespectively disposed on the left, center and right of the vehicle, eachof which is receiving the electromagnetic waves from the lane marker.When the vehicle is driving in the center of the lane, the receivingantenna 2 receives stronger electromagnetic waves compared with theother antennas. In other wards, the detection circuit 17 connected tothe receiving antenna 2 detects stronger electromagnetic waves.

When the vehicle starts to deviate to the right, the receiving antenna 1disposed on the left of the vehicle begins to receive stronger signalthan other receiving antennas, and once it exceeds a certain level, thelateral deviation monitor judges that the distance between the vehicleand the lane marker has exceeded a predetermined threshold and alertsthe driver.

Likewise, when the vehicle starts to deviate to the left, the strengthof the electromagnetic waves received in the receiving antenna 3disposed in the right of the vehicle becomes stronger compared withother receiving antennas.

The MPU 12 can also include a means for changing the referencedeviation, which contains a table showing the relationship between thespeed and amount of lateral deviation of the vehicle. In the case ofusing this means for changing the reference deviation, reference valuesfor lateral deviation can be set such that when driving at high speeds,an alarm is given with a small deviation and when driving at low speeds,a larger lateral deviation is allowed before alerting. This enhancessafety for high-speed driving since alerting can be given even with aslight lateral deviation when driving at high speeds. For example,different reference values can be set for three stages of speed; up to60 km/h, 60-80 km/h, and over 80 km/h, so that warnings can be sent outwith smaller deviations as speed increases.

Furthermore, if a lateral-deviation-sensitive alarm, which issuesdifferent levels of warnings according to the amount of lateraldeviation detected by the lateral deviation monitor, is adopted, thedeviation of the vehicle can be shown, for example, in the followingmanner:

1) deviation up to a value “a”, a green lamp lights up;

2) deviation between the value “a” and a value “b”, yellow lamp blinksto announce the beginning of a deviation; and

3) deviation over the value “b”, a buzzer starts to warn the deviationfrom the driving line is large.

The lower the position of the electromagnetic wave lane marker detectoris, the lower the output that is required to detect the lane marker. Theheight of the vehicle changes depending on the number of passengers andamount of load. Based on this point, by introducing an output controlmeans related to the height of a vehicle, and setting predeterminedoutput levels of the transmitting amplifier in accordance with theheights of the vehicle detected by a height sensor, the best outputlevel can be selected for the height. The sensor used for such outputcontrol means can detect the height either from the suspension of thevehicle or the travelling of the electromagnetic waves from the vehicleto the road and the road to the vehicle.

FIG. 8 shows a structure of the vehicle positioning system in accordancewith a preferred embodiment of the present invention. Lane markers 19are laid under a road 18 in regular intervals, and a vehicle 20 has atransmitting antenna and receiving antenna 22 in the front and adetector unit 23 inside the vehicle. The vehicle detects and identifiesthe lane markers 19 as it runs. The detector unit 23 comprises an MPU, atransmission amplifier, receiving amplifiers, a detector circuit andpower supply circuit. Needless to say, when a plurality of receivingamplifiers are used a detectable area can be expanded.

The vehicle positioning system of this embodiment can be achieved byfreely combining the foregoing electromagnetic lane markers and lanemarker detectors.

As thus far described, the lane markers of the present invention canreflect the electromagnetic waves whose frequency is different from thatof the electromagnetic waves they receive. Therefore, the detector canreceive and detect the electromagnetic waves reflected from the lanemarker without interference from its own electromagnetic waves. Thus,the detector can provide a sufficient detection sensitivity and adetection distance as a device to be mounted on a vehicle.

Since the lane markers of the present invention transmit reflectedelectromagnetic waves only when it receives an exciting electromagneticwave transmitted by the detector mounted on the vehicle, they do nothave any influence on objects surrounding them. As such, a vehiclepositioning system does not require further maintenance.

INDUSTRIAL APPLICABILITY

The lane markers of the present invention can reflect electromagneticwaves of the frequency deferent from that of the electromagnetic wavesthey received. Therefore, the detector can receive and detect theelectromagnetic waves reflected from the lane marker without beinginfluenced by its own electromagnetic waves. Thus, the detector cansurely provide a sufficient detection sensitivity and a detectiondistance as a vehicle mounted device.

Since the lane markers of the present invention transmit reflectedelectromagnetic waves only when it receives exciting electromagneticwaves sent from the detector mounted on the vehicle, they do not haveany influence to objects surrounding them. Due to this, a vehiclepositioning system of the present invention does not require furthermaintenance.

What is claimed is:
 1. An electromagnetic lane marker comprising; anelectronic resonator comprising a cyclic coil connected to a capacitor,said electronic resonator resonates an inductive electromagnetic wave ofa first frequency; and a frequency conversion circuit coupled to saidelectronic resonator, said frequency conversion circuit converts theelectromagnetic wave of the first frequency to an electromagnetic waveof a second frequency and transmits the electromagnetic wave of thesecond frequency, said second frequency being different from said firstfrequency.
 2. The electromagnetic lane marker of claim 1, furthercomprising a second cyclic coil for transmitting the electromagneticwave of the second frequency.
 3. The electromagnetic lane marker ofclaim 1, wherein said electronic resonator further comprising capacitorsconnected to both ends of said first cyclic coil, and said electronicresonator, said frequency conversion circuit and said second cyclic coilare stored in a sealing container made of a non-magnetic material. 4.The electromagnetic lane marker of claim 3, wherein said sealingcontainer is a cylinder with a lid and a base.
 5. The electromagneticlane marker of one of claims 2 to 4, wherein said first cyclic coil andsaid second cyclic coil comprise loop antenna and bar antenna,respectively.
 6. The electromagnetic lane marker of one of claims 2 to4, wherein said first cyclic coil and said second cyclic coil comprisebar antenna and loop antenna, respectively.
 7. The electromagnetic lanemarker of claim 2, wherein said first cyclic coil and said second cycliccoils are disposed at right angles.
 8. The electromagnetic lane markerof one of claims 1 to 4 further comprising a frequency multipliercircuit which converts the first frequency to the second frequencyhaving a frequency which is multiples of the first frequency.
 9. Theelectromagnetic lane marker of one of claims 2 to 4, wherein said secondcyclic coil has a L-tap structure, where the L-tap structure means acoil having a tap therein.
 10. The electromagnetic lane marker of one ofclaims 2 to 4, wherein said second cyclic coil has a C-tap structure,where, the C-tap structure means a capacitor circuit having a connectingpoint between at least two capacitors.
 11. The electromagnetic lanemarker of one of claims 1 to 4, wherein said frequency conversioncircuit comprises rectifiers connected parallel with each other.
 12. Theelectromagnetic lane marker of one of claims 1 to 4, wherein saidfrequency conversion circuit comprises a diode bridge.
 13. Anelectromagnetic lane marker according to claim 1 wherein said electronicresonator is included in a passive circuit.
 14. An electromagnetic lanemarker detector for transmitting a first electromagnetic wave of aspecified first frequency, said electromagnetic lane marker detectorhaving a means for identifying and receiving an electromagnetic wave ofa second frequency transmitted from an electromagnetic lane marker, saidelectromagnetic lane marker comprises: an electronic resonator; afrequency conversion circuit coupled to said electronic resonator, whichconverts said first electromagnetic wave to said electromagnetic wave ofthe second frequency, said electromagnetic lane marker having separateantennas for receiving said first electromagnetic wave and fortransmitting said electromagnetic wave of the second frequency.
 15. Theelectromagnetic lane marker detector of claim 14, wherein an antennatransmitting the electromagnetic wave of the specified first frequencyand the antenna receiving the electromagnetic wave of the secondfrequency comprise a loop antenna and a bar antenna, respectively. 16.The electromagnetic lane marker detector of claim 14 or 15, wherein ameans for transmitting electromagnetic waves of the specified firstfrequency comprises a 8-letter-shaped loop antenna.
 17. Theelectromagnetic lane marker detector of one of claims 14 or 15 furthercomprising; a plurality of receiving antennas which receiveelectromagnetic wave of a specified second frequency; and a positiondetector for detecting positions of said receiving antennas with respectto the lane markers, said position detector comparing each strengths ofsaid electromagnetic waves received by said plurality of receivingantennas.
 18. The electromagnetic lane marker detector of one of claims14 or 15, further comprising: a lateral deviation monitor which monitorsan amount of lateral deviation from a lane marker; and an alarm whichwarns when lateral deviation exceeds a predetermined threshold.
 19. Theelectromagnetic lane marker detector of claim 18 further comprising ameans for changing an amount of a reference deviation, said means forchanging the amount of the reference deviation being capable of changingthe threshold of lateral deviation with respect to the lane marker, andsaid threshold being a reference for the alarm.
 20. The electromagneticlane marker detector of claim 18 further comprising an alarm whichalerts the driver through one of an indicator, a buzzer, a voicenotification and vibration.
 21. The electromagnetic lane marker detectorof claim 18 further comprising a lateral-deviation-sensitive warningmeans which changes a content of an alert according to an amount oflateral deviation with respect to the lane markers.
 22. Theelectromagnetic lane marker detector of one of claims 14 or 15 furthercomprising a velocity-sensitive transmitting means for detecting thevelocity of a vehicle on which the detector is mounted, wherein saidvelocity-sensitive transmitting means stops transmitting electromagneticwave of said first electromagnetic wave of a specified frequency whenthe velocity of the vehicle is slower than a predetermined value andresumes transmitting when the velocity exceeds the predetermined value.23. The electromagnetic lane marker detector of one of claims 14 or 15further comprising a vehicle-height-sensitive output controlling meanswhich, when a height of a vehicle is set, changes transmitting outputlevels by controlling a transmitting amplifier according to the setvalue.
 24. The electromagnetic lane marker detector of one of claims 14or 15, further comprising a vehicle-height-sensitive output controllingmeans which detects the height of the vehicle and changes transmittingoutput levels by controlling a transmitting amplifier according to thedetected height.
 25. An electromagnetic lane marker detector accordingto claim 14, wherein said electronic resonator is included in a passivecircuit.
 26. A vehicle positioning system based on: A) anelectromagnetic lane marker comprising; an electronic resonatorcomprising a cyclic coil and a capacitor, said electronic resonatorresonates an inductive electromagnetic wave of a first frequency; and afrequency conversion circuit coupled to said electronic resonator, saidfrequency conversion circuit converts the electromagnetic wave of thefirst frequency to an electromagnetic wave of a second frequency andtransmits the electromagnetic wave of the second frequency, saidelectromagnetic lane marker having separate antennas for receiving saidfirst electromagnetic wave and for transmitting said electromagneticwave of the second frequency; and B) an electromagnetic lane markerdetector for transmitting the electromagnetic wave of the firstfrequency, said electromagnetic lane marker detector having a means foridentifying and receiving the electromagnetic wave of the secondfrequency transmitted from said electromagnetic lane marker.
 27. Thevehicle positioning system of claim 26, wherein said electromagneticlane marker is laid under a road.
 28. The vehicle positioning system ofclaim 26, wherein said electromagnetic lane marker is laid under a roadat predetermined intervals to support automatic driving.
 29. A vehiclepositioning system according to claim 26, wherein said electricresonator is included in a passive circuit.